An electromagnetic type retarder for obtaining a brake torque by utilizing an electric eddy current is publicly known as shown in the Japanese patent application Laid-Open No. 125219/2008.
FIG. 5 to FIG. 7 herein depicts show a conventional self generation electromagnetic type retarder, wherein a reference numeral 1 denotes a tire of a car, 2 denotes a starter, 4 denotes an alternator, and 5 denotes an electromagnetic type retarder. The electromagnetic type retarder 5 comprises a main portion 6, a control device 8 for processing an operation signal 7, and a driving device 10 consisting of transistors T1 to T3 opened and closed by a drive pulse 9 from the control device 8, respectively.
The main portion 6 comprises a stator yoke 11, a stator 12 having magnetic coils L1 to L12, each having an iron core, arranged along a circle and spaced apart from one another, a steel rotor (drum) 13 surrounding the stator 12 and rotated according to the rotation of the tire 1, and fins 14 provided on the outer peripheral surface of the drum 13.
The magnetic coils L1 to L12 form three-phase connections of A phase, B phase and C phase.
Each of the magnetic coils L1, L2, L3, L7, L8 and L9 is opposite in polarity to each of the magnetic coils L4, L5, L6, L10, L11 and L12.
According to the conventional retarder, the drive pulse 9 is generated when the operation signal 7 is applied to the control device 8, so that the transistors T1 to T3 of the driving device 10 are turned ON, and resonance circuits consisting of magnetic coils L1 to L12 and capacitors C are formed.
An electric voltage induced in the magnetic coils by the residual magnetic field of the drum 13 becomes a three-phase AC voltage of a specific frequency by the function of the resonance circuits consisting of the magnetic coils and the capacitors, when the revolution number of the drum 13 becomes faster than that of the rotary magnetic field calculated from the resonance frequency of the magnetic coils and the capacitors. In this state, an eddy current is generated in the drum 13 according to the difference between the revolution number Ns of the rotary magnetic field generated by the three-phase AC voltage and the revolution number Nd of the drum 13. By the eddy current generated in the drum 13, the voltage of the magnetic coils is increased, so that the eddy current generated in the drum 13 is further increased.
The increase of the eddy current function is stopped at a point that the magnetic field is not increased even if the voltage of magnetic coils is increased. The eddy current in the drum 13 generates a joule heat, so that a larger braking power is applied to the drum 13. The braking energy is converted into heat and the heat is radiated into the atmosphere from the fins 14 provided on the outer peripheral surface of the drum 13.
A diesel engine prominently used as a commercial car engine has additionally an automatic stop device or an auxiliary heating device as described in the Japanese Utility Model Application Laid-Open No. 65024/1994, because such use of a diesel engine is repeatedly idled or run for a short time. A large electric power is required for such additional device and accordingly it is necessary to use an additional power source or an alternator; this results in an increase of weight and cost.
FIG. 8 is a graph indicating the relationship between an electric current passing through the electromagnetic coils and a voltage induced in the electromagnetic coils when the revolution number of the steel rotor becomes faster than that of the rotary magnetic field. In FIG. 8, a reference symbol A denotes a saturated point of the voltage induced in the electromagnetic coils, an impedance line extending from the point A denotes a voltage which is impossible to take out because an electric energy is consumed in the electromagnetic coils, a reference symbol B denotes an unsaturated point, and a reference symbol C denotes a point on the impedance line corresponding to the point B. The voltage difference between the points B and C becomes an electric power Pout which is possible to take out. Pout=C (VB2−VC2)/T0, where C is a value of capacitor, VB is a voltage at the point B, VC is a voltage at the point C, and T0 is a period.
According to experiments and study by the inventor, a self generation electromagnetic type retarder shown in FIG. 5 to FIG. 7 has a very high power generating ability, and it is possible to supply a power three times larger than the power of the alternator, without increasing the weight and cost, and it is possible to supply to the additional device as mentioned above a high AC voltage or low DC voltage.
Further, the inventor has determined that the induced voltage directly after the start of the retarder is so small that no electric power can be supplied as shown in FIG. 3 and FIG. 8.
The present invention can be obtained on the basis of the above facts.